Optical components are now being integrated in chips along side microelectronic components. An example of one such approach is described in U.S. Ser. No. 10/280,505, entitled “Optical Ready Substrates,” incorporated herein by reference. Basically, it is a semiconductor wafer into which optical signal distribution network made up of optical waveguides, optical detectors, and other optical components has been fabricated in anticipation of the subsequent fabrication of microelectronic circuitry above the optical network. The optical sign distribution network is designed to carry optical signals (e.g. clock or data signals) to and from the microelectronic components that will be fabricated above the optical circuitry.
In general, the optical components that are used in these IC chips require smooth surfaces. For redirecting light, optical surfaces must also often have a smooth curvature or a smooth transition from one plane to another. Such surfaces must often be disposed at angles apart from planar surfaces often used in thin-film processing.
Previous researchers have attempted to make smooth dry etched surfaces at 45° from the sample surface with little success. Such attempts at dry etches generally involved a substantial flow of sidewall passivation gas combined with the etching gas to form a tapered sidewall.
Other optics groups have resorted to ordering specially cut off-axis crystalline wafers and using a crystal-plane-selective wet etch to achieve 45° sloped surfaces. The main problem is that it requires a non-standard wafer. Performing this etch using an off-the-shelf <100> oriented wafer will yield a 54.7° angle.
There continues to be a need for a process that provides greater control over the fabrication of these and other 3D features.